Such devices are included in portable payment terminals, for example, within an electronic security application module (SAM). These modules are very important because they contain secret information (example: bank keys), the discovery of which would allow access to an entire system.
The information is necessarily in an electronic layer of an integrated circuit. A passivation layer generally covers the electronic layer.
In some cases, this layer may not be a sufficient obstacle to access to the secret information, if sophisticated reading means are employed to read the information through the passivation layer. These reading means can utilize particle beam-type scanning techniques, for example.
Existing techniques intended to protect such information include the use of conventional intrusion sensors to protect an enclosure containing the electronic memory containing the information.
Also known in themselves are means protecting the integrated circuit directly against reading with the aid of sophisticated equipment. Said means are of two types: the first consists in masking the pattern of the semiconductor, for example by a metalization, a grid of dummy circuits or a diamond carbon layer; the second consists in memorizing the information in a RAM type memory and possibly combining it with random numbers that are changed continuously. The information is accessible only through an operating system that controls access to it. The principles used are identical to those of microprocessor cards. With this second type of means, the secrets contained in a RAM are always lost if the power supply to the component is interrupted. In this case, access to the information is not totally impossible providing the following are known:
how to eliminate the resin from the casing of the component when live, without creating a short-circuit that would lead to loss of the information, PA1 the exact schematic of the component, PA1 the memory "scrambling" table, PA1 the address of the secrets in the memory plane, and PA1 the correct manner of writing and reading the address bus and the data bus in real time.
The various prior art techniques mentioned hereinabove have the disadvantage of being ineffective if highly sophisticated means are employed or of being costly, in particular when diamond carbon masks are used.